Microtubules (MTs) are ubiquitous in eukaryotic cells where they form diverse organelles involved in cell shape, cell motility, intracellular movements mitosis and meiosis. Among the most elaborate microtubular organelles are basal bodies and the axonemes of cilia and flagella, which, in humans, are found in the respiratory tract, the female reproductive tract, and in tissues with high incidences of cancer. Ciliary dysfunction can cause respiratory and fertility problems. The long-term goals of this proposal are to understand the molecular mechanisms underlying microtubule diversity with particular emphasis on the biogenesis and function of cilia and basal bodies. Having identified specific "axonemal sequences" as the sites of glyclylation in both alpha- and beta-tubulins, we will identify and characterize the function of other primary sequences and post-translational modifications (PTMs) of tubulins in specifying the structure and function of MT organelles. The lower eukaryote, Tetrahymena thermophila, is used as a model. Advantages of this system include its relatively small tubulin multigene superfamily and the recent development of methods for mass transformation of somatic and germinal nuclei, enabling gene replacement and gene disruption. These methods will be used for a detailed mutagenic analysis of the function of alpha-, beta-, and gamma-tubulin and of their secondary modifications. The mechanisms by which a newly discovered, unusually diverse beta-tubulin is targeted to specific MT organelles will be analyzed. The mechanism by which glycylation affects ciliary MT function will be studied by using genetic and biochemical approaches to identify and characterize proteins that interact specifically with glycylated tubulin. These studies should shed light on normal cilia biogenesis and the function of tubulins in generating MT diversity, that are required to understand cytoskeletal functions that are critical for normal development and that are frequently abnormal in neoplastic cells.